A Study and Optimization of Complexation of Cobalt Ions with Dihydroquercetin in Aqueous Solutions

Abstract

This work continues a series of studies devoted to complex formation of ions of biogenic metals with the flavonoid dihydroquercetin (DHQ). The interaction of Со2+ ions with DHQ in aqueous solutions has been investigated. It has been found that, at different pH of a solution, complex compounds (CC) with different stoichiometry are formed; a variation of the pH value of a solution from 6.0 to 7.0 results in the formation of compounds (1)–(3) with the metal : flavonoid ligand ratio (Met : L) from 1 : 2 at рН 6.0 (1), through 2 : 3 at pH 6.4–6.7 (2), to 1 : 1 at рН 6.8–7.0 (3). By using the thermogravimetric method and the data of the elemental analysis, the most probable composition of the compounds with the determination of the amount of bound water has been proposed: [CoL2(H2O)4] for (1), [Co2L3(ОН)(H2O)4] for (2), and [CoL(ОН)(H2O)2] for (3). Conditions for the optimization of product yield in the complexation reaction of Со2+ ions with DHQ in an aqueous solution have been determined for compound (2): the рН value of solution 6.7; the reaction time 15 min; the temperature of the reaction solution 90°С; the molar ratio of the initial reagents DHQ : Со2+ 1 : 1.5; the initial concentration of DHQ 0.020 mol/L and that of Со2+ 0.030 mol/L; and the use of CoSO4 ⋅ 7H2O as a source of cobalt ions. The yield of the product is 81.8%.